1. Field of the Invention
This invention relates to feeding of material into a furnace and, in particular, to feeding glass batch material from a rotary kiln through a transition section and into a glass melting furnace while exhaust gas from the furnace preheats the batch material in the rotary kiln.
2a. Technical Considerations
It has long been recognized that exhaust gas from a combustion heated glass melting furnace or other melting process furnace contains large amounts of thermal energy that can be recovered to improve the overall efficiency of the process. Conventionally, regenerators and recuperators have been employed to recover heat from melting process furnaces by preheating combustion air, but their efficiency is less than desired. Instead of preheating combustion air by way of regenerators or recuperators, it has been proposed to recovery waste heat by means of preheating the feed material.
Using the waste heat from the melting furnace to preheat the batch material can lead to certain complications. It is believed that during the melting process certain components of the batch material may become vaporized and may be carried out of the furnace by the exhaust stream along with any particulate matter that may become entrained in the gas. The vaporized materials may condense on an interior surface of a preheating vessel or in a transition section that links the preheating vessel with the melting furnace for passage of the hot exhaust gas therethrough. When condensation occurs, the condensed vapors may leave a glassy, sticky deposit. The particulate matter may soften and also become a sticky deposit due to its exposure to the hot temperature exhaust gas. Accumulation of these sticky deposits may cause buildup of batch material as it moves through the kiln resulting in the clogging of the batch feed arrangement. Furthermore, entrained particulates may accumulate on deposits in the transition section and affect the preheating arrangement.
In U.S. Pat. No. 4,381,934 to Kunkle and Matesa, there is disclosed an intensified batch liquefying process in which large volumes of batch are efficiently liquefied in a relatively small space. This type of process, particularly when using intensified heat sources, produces relatively small volumes of high temperature exhaust gas. This exhaust gas can be recovered and used to directly heat the batch stream so as to improve the efficiency of the process. It is desirable to be able to direct the preheating exhaust gas as it passes from the batch liquefier to the kiln away from surfaces which tend to collect material in the exhaust gas stream so as to minimize clogging in the rotary kiln and the exhaust gas passageway from the liquefier to the kiln.
2b. Patents of Interest
U.S. Pat. Nos. 4,375,236 and 4,506,726 to Tsai teach the use of air jets to redistribute the air flow in a regenerative furnace for melting glass batch material. Air jets positioned in the gas distributing space of the regenerators modify air flow so that air Passing through the packing is evenly distributed throughout the packing to prevent localized overheating.
U.S. Pat. Nos. 4,496,315 to Savolskis and 4,496,316 to Tsai teach the use of air jets for controlling the flow of the air into and out of the melting chamber of a regenerative furnace. In one embodiment the air jets are positioned in the target wall of the regenerator and are directed at selected firing ports. The jets can be used to either increase or reduce the air flow from the regenerator into the chamber through selected firing ports. In another embodiment, angled air jets can be positioned directly in the firing ports to increase or decrease air flow.